1. Field of the Invention
The present invention relates to a connecting structure for high voltage resistance wire which is suited for connecting a high voltage resistance wire for suppressing noise, in particular to a wire connecting structure which is suited for feeding a high voltage to the ignition plug of an engine or the like.
2. Description of Prior Art
Conventionally, for feeding a high voltage to the ignition plug of an engine or the like, a high voltage resistance wire for suppressing noise is provided with a connector to the high voltage terminal. A rubber cap is then adhered to the connecting portion, covering and hermetically sealing the connector to the high voltage terminal. An example of such a prior structure is shown in FIG. 1. In the figure, 1 is an ignition terminal plug, 2 is an ignition plug insulator, 3 is a high voltage resistance wire for suppressing noise, 4 is a connector terminal which is secured to one end of the high voltage resistance wire 3, and 5 is a plug cap made of rubber which is fitted to the circumference of the end of the high voltage resistance wire 3 so as to enclose the terminal therein. The plug cap 5 makes a close contact with the exterior of the ignition plug insulator 2 to prevent the attachment of moisture or contaminants to the surface of the insulator, thereby suppressing the leakage of electricity at high voltage or generation of short-circuiting by flashing.
In such a conventional connecting structure, the electrical insulation of the connecting portion is maintained by a compressive adhesion of the plug cap to the ignition plug insulator by elasticity of the rubber of the plug cap. Lately, however, along with the rise in the compression ratio of the engine or the trend of making turbo engines, the ignition voltage is inclined to be set at higher values, which demands a securer electrical insulation at the connecting portion. Accordingly, a reduction in the dielectric strength due to degradation of the sealing property of the ignition plug is becoming a serious concern. Such decrease in the sealing property of the ignition plug is considered to be caused by the reduction in the elasticity of rubber due to thermal aging of the plug cap, creeping, or a deterioration of the rubber surface.